The present invention is directed to a tension member for use as a rock anchor or the like and also to a method for forming the tension member
Rock anchors are used to secure a mass of rock against shifting at the earliest possible time when driving tunnels or similar cavities into natural stratified rock formations with open seams or crevices. Typically, such rock anchors are subjected to a combination of tension and shearing stresses when one part of the rock mass moves relative to another. Tension members used as rock anchors must be able to deform under the considerable deforming forces developed. The stiffness of a solid cross-section of the tension member, such as in a steel rod, can be an obstacle to the absorption of the deforming forces.
Tubular shaped tension members formed of steel with thin walls have been known which have been pressed by hydraulic pressure against a borehole wall for transmitting forces through friction. Such tubular shaped tension members have an even lower resistance to shear than rod-shaped tension members or anchors, however, they do afford greater shear travel since the borehole containing the tension member remains essentially free. Tubular shaped tension members have no corrosion protection and can not be fabricated in random lenghts. Anchor members can not be secured to the smooth outer surfaces of such members.